Gas lift system



E. RICH GAS LIFT SYSTEM Dec. 9, 1969 2 Sheets-Sheet l Filed NOV. l5, 1957 ELVIS RICH I INVENTOR.

BY a.'

ATTORNEY f De. 9, 1969 Filed Nov. 13, 1967 RICH - GAS LIFT SYSTEM 2 Sheets-Sheet 2 ELV/s RICH JNVENTOR.

V- BYWQaQh-L ATTORNEY United States Patent O 3,482,526 GAS LIFT SYSTEM Elvis Rich, Houston, Tex., assiguor to Esso Production Research Company, a corporation of Delaware Filed Nov. 13, 1967, Ser. No. 682,443 Int. Cl. F04f 1/08, l/20 U.S. Cl. 103-234 13 Claims ABSTRACT OF THE DISCLOSURE Apparatus for the intermittent gas lifting of liquid from a well including a string of tubing containing a port in the tubing wall near the lower end thereof, two packers spaced to form an annular chamber near the lower end of the tubing string, a valve in the lower end of the tubing for admitting liquid from the formation into the tubing and chamber, and means for alternately injecting gas down the tubing into the chamber and producing liquid from the chamber up the tubing to the surface.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to the use of gas to lift liquid from a borehole in the earth and is particularly concerned with an intermittent gas lift system for use in oil wells and similar boreholes.

Description of the prior art Intermittent gas lift systems have been widely used to produce crude oil from wells penetrating low-pressure subterranean formations. Most of the systems currently employed require the injection of gas into the annulus between the production tubing and casing under sufcient pressure to force it through one or more gas lift valves located in the tubing string below the oil level. This gas which thus Hows into the tubing lifts slugs f oil upwardly to the surface. By controlling the gas injection rate, pressure, and other Variables, fluids can often be produced at relatively lost cost without the necessity for installing a pump.

Where more than one productive formation is penevtrated by the well, use of the annulus to conduct the lifting gas and the tubing to conduct the lifted liquids is precluded if segregation of produced fluids is to be maintained. In this situation, existing systems require an additional string of tubing so that three separate passages are available for the lifting gas and the segregated produced iiuids. The additional investment and maintenance necessitated by the installation of the second string of tubing is undesirable. Moreover, where small-diameter well casing has been installed, space limitation may make installation of a second tubing string impracticable.

SUMMARY OF THE INVENTION This invention provides an improved gas lift system which alleviates the problems outlined above. The system of the invention utilizes an annular chamber between the tubing and the casing into which the produced fluids are directed. After production has accumulated in this chamber for a sufcient period of time, high-pressure gas in injected down the tubing string and into the upper part of the chamber. The tubing is then vented into a low-pressure liquid gathering line, causing the gas stored in the upper part of the chamber to expand and force the liquid from the chamber up the tubing to the surface.

The apparatus used in carrying out the invention normally includes a string of tubing or other conduit vertically suspended within the borehole, packers for sealing oif a cased section of the borehole to create an annular chamber about a port in the tubing wall near the bottom of the 3,482,526 Patented Dec. 9, 1969 ice string, a directional choke mounted in the tubing adjacent to the top of the chamber, a check Valve in the bottom of the tubing, and means for alternately connecting the upper end of the conduit to a high-pressure gas line and a lowpressure liquid gathering line.

The gas lift system of the invention is advantageous in that fluid can be gas-lifted from an oil well with a single string of tubing, leaving the casing-tubing annulus free for other purposes. When used in single-zone producing wells, the major part of the casing is not subjected to high pressures. This reduces difficulties due to casing leaks. In addition, less downhole equipment is required than is generally necessary for existing gas lift systems, resulting in increased economy. The gas lift system of the invention thus has many advantages over systems employed heretofore.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 schematically illustrates the apparatus of the invention in a dual completion oil well as oil flows in the lower formation into the chamber, FIG. 2 depicts the well and apparatus of FIG. 1 as high-pressure gas is injected down the tubing into the chamber. FIG. 3 schematically represents the well and apparatus of FIGS. 1 and 2 as the high-pressure gas in the chamber expels liquid from the chamber to the surface. FIG. 4 is a cross-sectional elevation of a differential pressure actuated valve suitable for use in the gas lift system. FIG. 5 is a cross-sectional elevation of a directional choke of the type used in the system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The apparatus shown in FIGS. 1 through 3 of the drawing includes a borehole 11 drilled through nonproductive strata 12 and 13, through high-pressure oil-bearing zone 14, and into low-pressure oil-bearing formation 15. The wellbore contains a string of casing 16 which has been cemented into place with cement 17 to provide a fluid-tight seal which prevents the escape of connate uids from one zone to another. The casing and surrounding cement have .been perforated as indicated by reference numbers 18 and 19 to provide communication between the interior of the casing and the oil-bearing formations. A string of production tubing 20 has been suspended in the wellbore from a tubing hanger, not shown, in wellhead 21 to a point within the lower producing zone. Packer 22 is set below highpressure oil-bearing zone 14 and forms pressure-tight seals With the casing 16 and production tubing 20. This packer both contines production from high-pressure zone 14 to the casing-tubing annulus and forms the upper end of annular accumulation chamber 23. Packer 24, which is also located between the tubing string and the casing, is set below packer 22 to form the lower end of the accumulation chamber. Although shown at the lower end of the tubing string, the chamber is not limited to this position within the borehole. Instead, it may be located at any point between the lower end of the tubing and the surface, limited only by the requirements that reservoir pressure be sufcient to produce Huid into the chamber and that the chamber must not interfere with production from other zones.

A differential pressure actuated valve 25 is shown mounted in the lower end of the production tubing fin FIGS. l-3. A preferred valve assembly is shown in FIG. 4. In this assembly, valve 41 is biased by adjustable spring 42 against seat 43. The valve is normally closed and opens only when formation pressure acting against the bottom ofthe valve through port 44 exceeds tubing pressure which is in communication with the top of the valve through port 45 by a sufficient amount to overcome the bias of spring 42. The upper end of the valve assembly is threaded to accommodate a conventional wireline setting tool which will anchor the valve in the tubing and from a pressure-tight seal with the tubing wall, but will permit the valve to be retrieved and replaced with wireline equipment. One suitable wireline tool is the Camco C lock, manufactured by Camco, Inc., of Houston, Tex., and shown in volume 1 of the 1966-67 Composite Catalog at page 1120. In lieu of such an assembly, an unbiased standing valve which would allow flow from the formation into the tubing, but prevent ilow in the opposite direction, could be used in the bottom of the tubing string. These are commercially available from a number of sources, but are typified by the standing valves manufactured by Camco, Inc. of Houston, Tex., and illustrated in volume 1 of the 1966-67 Composite Catalog at page 1123.

The production tubing communicates with accumulation chamber 23 through opening 26 which is located in the tubing string at a depth slightly above the bottom of the chamber as shown in FIGS. 1-3. Preferably a perforated or slotted sub is used lfor this purpose.

Directional choke 27 is mounted in the tubing string at a depth corresponding to the top of accumulation chamber 13 as shown in FIGS. 1-3. A preferred choke assembly is illustrated in FIG. 5, in which valve 51 is biased by adjustable spring 52 against seat 53. Port 54 exposes the top of the valve to tubing pressure while port 55 exposes the bottom of the valve to chamber pressure. This valve permits high-pressure gas to freely flow from the tubing into the chamber, but restricts ow in the other direction. Small-diameter port 56 always remains open but restricts flow to a low rate. The combination of spring-loaded valve S1 and port 56 creates a directional choke that permits free passage of iiuids from the tubing to the chamber but restricts flow in the opposite direction to low rates. So that the choke assembly can be removed by wireline equipment, it is mounted in a commercial gas-lift mandrel 57 and has a latching pickup sub 58 attached to its upper end. Suitable mandrels and subs are available commercially and are exemplied by the Camco, Inc. type MME mandrel and type R latch shown on page 1140 and 1121 of the 1966-67 Composite Catalog respectively.

Surface equipment utilized in the system of FIGS. 1-3 includes a Christmas tree 28 which is connected to wellhead 21 and includes the usual pressure gauges, flow meters, and other equipment not shown. Line 29 communicating with the casing-tubing annulus leads from the Christsmas tree to a owline, separation equipment, and storage with are not shown. Line 30 communicating with the production tubing extends from the Christmas tree to two-position, directional valve 31. In one position, shown in FIG. 2, the valve leads to line 32 which is connected to a high-pressure gas source. In its other position, FIGS 1 and 3, the valve leads to owline 33 which is connected to low-pressure separation equipment and storage facilities, not shown. The valve position is governed by controller 34.

Referring now to FIG. l, the well is depicted with produced iiuids entering the chamber 23. Valve 31 is open to low-pressure owline 33 which maintains low pressure in the tubing. Tubing pressure and chamber pressure equalize through directional chok-e 27. Pressure in formation 1S exceeds that of the production tubing and of the accumulation chamber causing differential pressure actuated valve to open. Produced fluid flows up through valve 25 into the production tubing which is in uid communication with the accumulation chamber through opening 26. The liquid level rises in the tubing and the chamber at the same rate since gas trapped in the chamber Willbe displaced through directional choke 27 into the tubing. When the liquid attains a high enough level above valve 25, its hydrostatic head will reduce differential pressure across valve 25 and valve 25 will close. This prevents the liquid from attaining such a height that high-pressure gas could not expel it from the chamber. Where a commercial standing valve is used in the bottom of the tubing string, the system should be operated so as to assure that the liquid level in chamber 23 does not rise too high. This can be accomplished by initiating production with very short producing periods and later lengthening the producing periods after the producing capacity has been determined.

At the end of a preset time period for production into the chamber, directional valve 31 is positioned by controller 34 to create communication between production tubing and high-pressure gas source line 32. As shown in FIG. 2, high-pressure gas ows into the tubing, rapidly increasing the pressure above differential pressure actuated valve 25, and closing the valve if it is still in the open position. The gas ows from the tubing into the upper section of chamber 23 through directional choke 27. When the pressure in the chamber is suicient to lift the collected fluid to the surface, controller 34 stops surface injection and opens directional valve 31 to llowline 33. Satisfactory gas injection could also be achieved by injecting gas at a known pressure and rate Ifor a preset period of time.

FIG. 3 illustrates the system when the pressurized downhole system is opened to the low-pressure owline. Tubing pressure rapidly decreases as the compressed gas surges through directional valve 31 into iiow 33. Directional choke 27 restricts the flow of gas from the upper section of the chamber to the production tubing to a very low rate. This forces gas trapped in the chamber to drive the liquid in the chamber into the tubing through 26 as it expands. Continued expansion of the gas propels the liquid up the tubing into the flowline. After the gas has discharged the liquid into the iiowline, the pressure in the tubing and chamber declines to that of the flowline and the production cycle is repeated.

Initially, it is preferable to manually alternate the position of valve 31 between high-pressure gas source line 32 and low-pressure liquid gathering line 33 extending the period for production into the chamber after each cycle. Once an optimum time period for production has been established manually, controller 34 can be programmed for this time period and automated operation can be initiated.

Throughout the above described intermittent gas lift cycle production from high-pressure oil-bearing zone 14 enters the casing-tubing annulus through perforations 18, flows up the annulus and out line 29 to separation equipment and storage. The ability to gas-lift oil through the tubing while producing another formation through the annulus illustrates one of the advantages of the invention over commercially available equipment which requires a second tubing string.

Although the concept of the invention is shown as applied to an oil well having two productive zones, it should be apparent that it is equally applicable to wells having only a single productive zone and in wells having several producing zones. Similarly, the system is not limited to gas-oil systems, but will work equally well in other fluid systems such as air-water and gas-water systems- What is claimed is:

1. Apparatus for intermittent gas-lifting of liquid from a borehole comprising:

(a) a conduit vertically suspended Within said borehole, said conduit having a lateral port near the lower end thereof;

(b) means for sealing olf a section of said borehole to form a substantially annular chamber surrounding the section of said conduit containing said port, said chamber extending upwardly from said port;

(c) means for admitting liquid from a producing formation into the bottom of said annular chamber, but preventing ow from said chamber to said producing formation;

(d) means for admitting gas into the upper part of said annular chamber from said conduit; and

(e) means for alternately connecting the upper end of said conduit with a pressurized gas line and with a liquid gathering line; whereby the same conduit which admits gas to said annular chamber is used to conduct production liquid from said chamber to the surface.

2. Apparatus as defined by claim 1 wherein said conduit is a string of production tubing and said chamber is formed in the tubing-casing annular by two packers.

3. Apparatus as defined by claim 1 wherein said means for admitting liquid from said producing formation into said chamber is a differential pressure actuated valve.

4. Apparatus as defined by claim 1 wherein said means for admitting liquid from said producing formation into said chamber is a standing valve.

5. Apparatus as defined by claim 1 wherein said means for admitting gas into the upper part of said annular chamber from said conduit is a directional choke.

6. Apparatus as defined by claim 1 wherein said means for alternately connecting the upper end of said conduit with said pressurized gas line and with said liquid gather ing line includes a controller that governs the time intervals between the injections of said gas and terminates injection of said gas when said tubing and said chamber attain a preset pressure.

7. Apparatus as defined by claim 1 wherein said means for alternately connecting the upper end of said conduit with a pressurized gas line and with a liquid gathering line includes a controller that governs the time interval between injections of said gas and terminates injection of said gas at the end of a preset time period.

8. Apparatus for intermittent gas-lifting of liquid from an at least partially cased borehole comprising:

(a) a tubing string vertically suspended within said borehole;

(b) two packers mounted on said tubing string to form a substantially annular chamber therebetween;

(c) a subjoint mounted in said tubing string adjacent to the bottom of said annular chamber and having ports therethrough;

(d) a directional choke mounted in said tubing string adjacent to the top of said chamber and oriented to restrict tiow from said chamber to said tubing string;

(e) a check valve mounted in said tubing string below said ports;

(f) a two-position, directional valve operatively connected to the upper end of said tubing string and cooperating therewith to connect said tubing string with a high-pressure gas line in one position and with a low-pressure liquid gathering line in the alternate position; and

(g) means for controlling the position of said two-position valve; whereby the same tubing strip that is used to admit high pressure gas to said chamber is used to conduct production liquid therefrom to the surface.

9. An apparatus as defined by claim 8 wherein said check valve is a differential pressure actuated valve.

10. An apparatus as defined by claim 8 wherein said means for controlling the position of said two-position valve includes a controller that governs the time intervals between injection of said pressure gas and terminates injection of said high-pressure gas when said tubing and said chamber attain a preset pressure.

11'. An apparatus as defined by claim 8 wherein said means for controlling the position of said two-position valve includes a controller than governs the time interval between injections of said gas and terminates injection of Said high-pressure gas at the end of a preset time period.

12. Apparatus for the intermittent gas-lifting of liquid from an at least partially cased borehole comprising:

(a) a tubing string vertically suspended within said borehole;

(b) two packers mounted on said tubing string sealably connecting said tubing to said casing and forming a substantially annular chamber therebetween;

(c) a subjoint mounted in said tubing string adjacent to the bottom of said annular chamber and having ports therethrough;

(d) a directional choke mounted in said tubing string adjacent to the top of said chamber and having its choke element oriented to restrict flow from said chamber to said tubing string;

(e) a check valve mounted in said tubing string below said ports; and

(f) means for alternately communicating the upper end of said tubing string with a high-pressure gas line and with a low-pressure liquid gathering line to alternately admit gas to said annular chamber and conduct liquid therefrom through the same tubing string.

13. A method of intermittently gas-lifting liquids from a well penetrating a producing formation and having a conduit suspended therein comprising:

(a) producing fluid from said formation into the lower end of a separate annular chamber surrounding said conduit until said chamber is partially filled with liquid;

(b) thereafter injecting pressurized gas down said conduit into the upper end of said chamber until a sufficient volume accumulates to lift the liquid contained in the lower part of the chamber to the earths surface;

(c) thereafter withdrawing gas from the upper end of said conduit until liquid lifted by gas from said chamber reaches the earths surface; and

(d) thereafter withdrawing liquid and gas from said chamber from the upper end of said conduit.

References Cited UNITED STATES PATENTS 749,563 l/1904 Johnson et al lr03-234 2,026,226 12/1935 Entrop 10S-234 X 2,142,481 l/l939 Stephens et al. 103-234 2,171,402 8/1939 Muir 10S-234 2,213,372 9/1940` Aucoin 103-234 X 3,288,081 l1/l966 McMillan 103-234 3,385,227 5/1968 Hart 103-232 X 3,410,222 11/1968 Swarton 103--238 X DONLEY J. STOCKING, Primary Examiner WARREN J. KRAUSS, Assistant Examiner U.S. Cl. X.R. 

